Field of the Invention
The present invention relates to an illumination device that is mainly used to control an illumination light path, and a display device.
Particularly, the present invention relates to an illumination device which realizes a simple manufacturing process as compared with a conventional process and uses an edge lighting system including a light guide body that realize a high degree of efficiency and a high degree of luminance, and a display device that is provided with the illumination device.
Description of the Related Art
A direct type illumination device and an illumination device using an edge lighting system are mainly adopted as a flat panel display or the like as typified by a recent liquid crystal television.
In the direct type illumination device, a plurality of cold-cathode tubes or LEDs (Light-Emitting Diodes), which serve as a light source, is regularly arranged on a back face of the panel.
A diffusion plate having a high degree of light scattering is used between an image display device such as a liquid crystal panel and the light source, and a configuration is adopted which causes cold-cathode tubes or LEDs which serve as a light source not to be visually recognized.
On the other hand, in the illumination device using an edge lighting system, cold-cathode tubes or LEDs are arranged at an end face (entry face) of a light-transmissive plate which is referred to as a light guide plate.
Generally, a light deflection element that effectively guides light entering the end face of the light guide plate to the emission face thereof is formed at a face (light deflection face) that is located on the opposite side of an emission face (face facing the image display device) of the light guide plate.
Currently, as a configuration of the light deflection element which is formed on the light deflection face, a configuration in which a white ink is printed thereon in a linear manner or in a scattered manner is generally known (for example, Patent Japanese Unexamined Patent Application, First Publication No. H1-241590 and Japanese Unexamined Patent Application, First Publication No. H3-6525).
In the light guide plate, since a light source is arranged at the end face of the transparent plate, an amount of light introduced into the region which is close to the light source is large, and an amount of light introduced into the region apart from the light source is relatively small.
Because of this, by arranging the light deflection elements so that the density of the light deflection elements (the number of the light deflection elements per unit area) is low at the position close to the light source and so that the density thereof is high at the position apart from the light source, a light guide is designed to uniformly emit light from the emission face.
Japanese Unexamined Patent Application, First Publication No. H3-6525 discloses a method of sparsely and densely arranging light deflection elements (a method of arranging the light deflection elements by adjusting an amount, a size, a position, a shape, or a density of the light deflection elements) and describes: a method of arranging the light deflection elements at a constant pitch while varying the sizes thereof; or a method of gradually varying arrangement intervals between the light deflection elements without varying the sizes thereof.
Most of light guide plates which are formed by a current printing method are produced using a method of arranging the light deflection elements at a constant pitch while varying the sizes thereof.
However, since light that is incident to a white dot is substantially uncontrollably and diffusely reflected, the emission efficiency thereof is low.
Additionally, it is not possible to exclude consideration of the light absorption due to the white ink.
Consequently, a method of forming micro lenses on a light deflection face of a light guide plate using an inkjet method, a method of forming light deflection elements using a laser ablation method, or the like, has been proposed in recent years.
Different from the case of using a white ink, since reflection, refraction, and transmission which are due to a refractive index difference between the resin of a light guide plate and air are used, light absorption hardly occurs.
For this reason, a light guide plate with a high level of light emission efficiency can be obtained as compared with a white ink.
However, similar to the printing of a white ink, since such light deflection elements which are formed using an inkjet method or a laser ablation method are formed in a different step after a light guide plate is shaped to be a flat plate, it does not mean that the number of processes is reduced.
Instead, the takt time of the step of using an inkjet method or a laser ablation method is longer than that of a step of printing a white ink, furthermore, there is a problem of an increase in cost such that the initial cost of equipment is high.
Consequently, a method has been proposed which shapes a light guide plate using an injection molding method or an extrusion molding method, and directly shapes light deflection elements during injection molding or extrusion molding (for example, Japanese Unexamined Patent Application, First Publication No. 2000-89033).
Since the light deflection elements are formed simultaneously with the shaping of the light guide plate, the number of processes is reduced, and cost reduction can be achieved.
However, when the light deflection elements are arranged while partially varying the density of the light deflection elements, it is difficult to gradually vary the sizes of the light deflection elements such as the case of the light guide plate using the aforementioned printing method.
Accordingly, a method is often adopted which partially adjusts (sparsely or densely adjusts) the density of the light deflection elements by gradually varying the arrangement intervals of the light deflection elements without varying the sizes thereof.
However, in the method of gradually varying the arrangement intervals of the light deflection elements, the arrangement intervals in two directions in a plane of the light deflection face are required to vary, and a layout design and manufacture of a die with reference to the layout design are extremely complicated.
In the case of adopting a method of fixing an arrangement interval in one direction (direction parallel to an incidence face of the light guide plate: X-direction) of the two directions and of only varying arrangement intervals in the other direction (direction orthogonal to the incidence face of the light guide plate: Y-direction) in order to facilitate the layout design, the following problem occurs.
Particularly, in a case where an interval in the X-direction is determined with reference to a low-density region adjacent to a light source (region having a low density of the light deflection elements), since the interval in the X-direction increases, it is not possible to sufficiently increase the density thereof in a high-density region apart from the light source, and an amount of light emitted from the emission face of the light guide plate decreases.
In contrast, in a case where an interval in the X-direction is determined with reference to a high-density region apart from the light source (region having a high density of the light deflection elements), since the interval in the X-direction decreases, an interval in the Y-direction is required to increase in the low-density region adjacent to the light source.
In this case, the light deflection elements are visually recognized in the low-density region, such as being aligned on a straight line parallel to the X-direction.
Japanese Unexamined Patent Application, First Publication No. 2003-43266 discloses a method of forming light deflection elements as a result of forming band-shaped regions on which dots (light deflection elements) are arranged at a constant pitch in both the X-direction and the Y-direction so that a band-shaped region having a high density of the light deflection elements is arranged at a position apart from a light source.
However, in the case of adopting such an arrangement, since the light deflection elements are arranged at a constant interval in the band-shaped region, a difference in amount of emission light between the portion close to the light source and the portion apart therefrom in the band-shaped region occurs, and a boundary between such band-shaped regions is visually recognized.
In order to solve this problem, it is necessary to reduce widths of the band-shaped regions in the Y-direction as much as possible so that it is not visible to the human eye; as a result, the number of band-shaped regions voluminously increases, and it does not contribute to simplification of a layout design and manufacture of a die with reference to the layout design.
Furthermore, even in the case where the light deflection elements are arranged as a result of partially adjusting (sparsely or densely adjusting) the density of the light deflection elements so as to make the configuration of the light deflection elements in the X-direction fixed and so as to vary the arrangement intervals in the Y-direction, there is another problem too.
FIGS. 14A and 14B illustrate an in-plane luminance distribution in the case where one light source or a plurality of light sources are arranged on two side end faces which are located opposite to each other and form a light guide plate, light deflection elements are arranged in a fixed manner in the X-direction, and light deflection elements are patterned (sparse-and-dense patterning) by partially adjusting (sparsely or densely adjusting) the density of the light deflection elements only in the Y-direction.
Light that is incident through an end face radially spreads to the inside of a light guide plate, and due to the influence of overlapping of the light sources, the influence of light reflection or light leakage from the end face on which the light source is not disposed, or the like, triangular regions G having a low luminance occur at the right and left in the in-plane thereof.
Generation of the above-mentioned dark region D is undesirable for surface illumination.
Accordingly, in a conventional light guide plate, since it is difficult to arrange the light deflection elements in the X-direction at a constant pitch, a design such that the number of light deflection elements increases in a locally-generated dark region is necessary, and a layout design of the light deflection elements become complicated.